The present invention relates to a roller contact device which includes a roller bridge-contacting two fixed contacts, a so-called bridge type roller contact.
Generally speaking, in roller contact devices which use a bridge type roller contact, an electric current path is formed between a first fixed contact and a second fixed contact via a roller. Since there are no sliding portions in contact with the roller it can rotate freely, electrolytic corrosion at the contact portions does not occur, and the smooth rotation of the roller can always be maintained.
However, when an increase in the capacity of current flow is desired for such a roller contact device, a plurality of roller contacts are arranged in parallel, either in an axial, travelling direction thereof, or in a coaxial combination.
FIG. 7(a) is a plan view of a conventional roller contact device as disclosed in Laid-Open Japanese Patent Application No. 62-52405, which consists of two sets of the first fixed contacts 1 and second fixed contacts 2, and roller contacts 3, each of which are arranged in the axial direction of the roller contacts 3 and connected in a parallel manner.
FIG. 7(b) is a perspective view of another conventional roller contact device as disclosed in Laid-Open Japanese Patent Application No. 62-52405, wherein two units of roller contact 3 are disposed in parallel in a travelling direction thereof.
FIG. 7(c) is a sectional view of another conventional roller contact device as disclosed in Laid-Open Japanese Patent Application No. 62-52405, wherein two units of roller contact 3 are arranged such that their barrels are in the form of coaxial cylinders.
In this way, in conventional roller contact devices, since multiple units of the roller contact 3 are disposed in parallel, either in an axial direction, a travelling direction, or in a coaxial combination, the two roller contacts, which are connected in parallel thus doubling the capacity of current flow.
As described in the foregoing, in conventional roller contact devices, since two units of the roller contact 3 are disposed in parallel in an axial direction thereof, the size of the roller contact device is doubled in terms of the axial direction; since two units of the roller contact 3 are disposed in parallel in a travelling direction thereof, the size of the roller contact device is doubled in terms of the travelling direction, which is disadvantageous to ensure insulation distance between adjacent fixed contacts; or, since two units of the roller contact 3 are in coaxial combination, the size of the device in an axial direction needs to be increased only slightly, but the diameter must be increased considerably, resulting in a large roller contact device in both axial and travelling directions of the roller contact. In either case, as two units of the roller contact 3 are disposed on the same side with respect to the first fixed contact 1 and the second fixed contact 2, contact reaction force is applied directly to fixed contact supporting members for the first fixed contact 1 and the second fixed contact 2 and a roller contact driving member as pressure. Therefore, the fixed contact supporting members and the roller contact driving member need to be structured such that they can withstand this pressure. In addition, as the number of roller contacts increases, the roller contact device becomes bulkier.